Tris(pentafluoroethyl)difluorophosphorane: A Versatile Fluoride Acceptor for Transition Metal Chemistry
Steffen A. Föhrenbacher, Mirjam J. Krahfuß, Ludwig Zapf, Alexandra Friedrich, Nikolai V. Ignat’ev, Maik Finze, Udo Radius
Abstract
Abstract Fluoride abstraction from different types of transition metal fluoride complexes [L n MF] (M=Ti, Ni, Cu) by the Lewis acid tris(pentafluoroethyl)difluorophosphorane (C 2 F 5 ) 3 PF 2 to yield cationic transition metal complexes with the tris(pentafluoroethyl)trifluorophosphate counterion ( FAP anion, [(C 2 F 5 ) 3 PF 3 ] − ) is reported. (C 2 F 5 ) 3 PF 2 reacted with trans ‐[Ni( i Pr 2 Im) 2 (Ar F )F] ( i Pr 2 Im=1,3‐diisopropylimidazolin‐2‐ylidene; Ar F =C 6 F 5 , 1 a ; 4‐CF 3 ‐C 6 F 4 , 1 b ; 4‐C 6 F 5 ‐C 6 F 4 , 1 c ) through fluoride transfer to form the complex salts trans ‐[Ni( i Pr 2 Im) 2 (solv)(Ar F )] FAP ( 2 a ‐ c[solv] ; solv=Et 2 O, CH 2 Cl 2 , THF) depending on the reaction medium. In the presence of stronger Lewis bases such as carbenes or PPh 3 , solvent coordination was suppressed and the complexes trans ‐[Ni( i Pr 2 Im) 2 (PPh 3 )(C 6 F 5 )] FAP ( trans ‐2 a[PPh 3 ] ) and cis ‐[Ni( i Pr 2 Im) 2 (Dipp 2 Im)(C 6 F 5 )] FAP ( cis ‐2 a[Dipp 2 Im] ) (Dipp 2 Im=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) were isolated. Fluoride abstraction from [(Dipp 2 Im)CuF] ( 3 ) in CH 2 Cl 2 or 1,2‐difluorobenzene led to the isolation of [{(Dipp 2 Im)Cu} 2 ] 2+ 2 FAP − ( 4 ). Subsequent reaction of 4 with PPh 3 and different carbenes resulted in the complexes [(Dipp 2 Im)Cu(LB)] FAP ( 5 a – e , LB=Lewis base). In the presence of C 6 Me 6 , fluoride transfer afforded [(Dipp 2 Im)Cu(C 6 Me 6 )] FAP ( 5 f ), which serves as a source of [(Dipp 2 Im)Cu)] + . Fluoride abstraction of [Cp 2 TiF 2 ] ( 7 ) resulted in the formation of dinuclear [FCp 2 Ti(μ‐F)TiCp 2 F] FAP ( 8 ) (Cp=η 5 ‐C 5 H 5 ) with one terminal fluoride ligand at each titanium atom and an additional bridging fluoride ligand.